there's loads of stuff you can do that doesn't go anywhere near a search engine. i used to write wordpress plugins, which ended up on other sites (i dont do that anymore, but it got a load of traffic). you can put together little ebooks of your site's subject too, and sell them for free in the apple store, and on amazon (i haven't personally tried amazon yet)
maybe you could put together some podcasts, if that fits your subject.
i'v been thinking of making an app too, for iphone and ipad, but i haven't got around to learning how to do it yet.
and i've got a sizeable amount of traffic from facebook and twitter as well, like loads of other people. most of my facebook and twitter stuff is automated, and is pulled straight from my site, so it's next to no work for me, but it still brings in the traffic.
you just need to branch out a bit, and try other techniques. most of them aren't as hard or as daunting as they might at first seem